Abstract
The experimenter who is confronted with the problem of natural resistance to poliomyelitis finds two avenues open for methodical approach. He can either investigate the agencies which are liable to cause changes in virulence of the etiological agent or he can attempt to study and correlate the different factors which modify susceptibility of the host. While there are reasons to suspect that host factors are more important in determining the course of events, the environmental conditions which may affect the virulence of the virus obviously lend themselves more readily to experimental analysis. It is a simple matter, for instance, to expose the virus to various physical and chemical agencies and to test for its survival or destruction by intracerebral injection into monkeys. Such studies have already contributed valuable data that are helpful in explaining the nature of the infectious agent. Thus, it has been shown that poliomyelitis virus possesses a very low thermal deathpoint 1 and that it is extraordinarily susceptible to the oxidizing or reducing action of certain chemicals. 2 On the other hand, the virus has proved quite resistant to exposure, to freezing, 3 drying,3 X-rays, 4 as well as sonic vibrations, 5 and remains relatively unharmed after contact with strong protoplasmic poisons. 6 Judging from these properties, the virus of poliomyelitis seems to resemble much more the toxins and ferments than the common animate agents of disease.
The literature offers very little information concerning the effect of ultraviolet light on the virus of poliomyelitis in vitro, although the light sensitiveness of other filtrable viruses, toxins and ferments has been well established. According to Flexner, 7 poliomyelitis virus is rapidly killed by sunlight, and Amoss 8 states that light in the presence of eosin destroys the virus.
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